Function write_ndx

io.c:2318–2362

Send a file-list index using a byte-reduction method. */

/* Send a file-list index using a byte-reduction method. */
void write_ndx(int f, int32 ndx)
{
	static int32 prev_positive = -1, prev_negative = 1;
	int32 diff, cnt = 0;
	char b[6];

	if (protocol_version < 30 || read_batch) {
		write_int(f, ndx);
		return;
	}

	/* Send NDX_DONE as a single-byte 0 with no side effects.  Send
	 * negative nums as a positive after sending a leading 0xFF. */
	if (ndx >= 0) {
		diff = ndx - prev_positive;
		prev_positive = ndx;
	} else if (ndx == NDX_DONE) {
		*b = 0;
		write_buf(f, b, 1);
		return;
	} else {
		b[cnt++] = (char)0xFF;
		ndx = -ndx;
		diff = ndx - prev_negative;
		prev_negative = ndx;
	}

	/* A diff of 1 - 253 is sent as a one-byte diff; a diff of 254 - 32767
	 * or 0 is sent as a 0xFE + a two-byte diff; otherwise we send 0xFE
	 * & all 4 bytes of the (non-negative) num with the high-bit set. */
	if (diff < 0xFE && diff > 0)
		b[cnt++] = (char)diff;
	else if (diff < 0 || diff > 0x7FFF) {
		b[cnt++] = (char)0xFE;
		b[cnt++] = (char)((ndx >> 24) | 0x80);
		b[cnt++] = (char)ndx;
		b[cnt++] = (char)(ndx >> 8);
		b[cnt++] = (char)(ndx >> 16);
	} else {
		b[cnt++] = (char)0xFE;
		b[cnt++] = (char)(diff >> 8);
		b[cnt++] = (char)diff;
	}
	write_buf(f, b, cnt);
}

/* Receive a file-list index using a byte-reduction method. */
int32 read_ndx(int f)